The present application relates to photovoltaic arrays for collecting solar energy to provide useful power, and more particularly to improved devices, systems and methods for diagnosing and monitoring such arrays.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Photovoltaic systems are one of the fastest growing sources of energy and are increasingly cost-effective. The cost and reliability of photovoltaic systems and their components, including photovoltaic modules and photovoltaic converters, continue to improve.
Photovoltaic modules and components are often in service for many years. An array or its components may be warranted for more than 20 years. While modules and other components are generally reliable, problems do arise. Over their service life, components are subject to malfunctions and/or performance degradation.
Various power monitoring systems are used to determine if actual performance meets projections. These power measurements can be: AC power at the output of the converter, DC power at the input of the converter, DC power at the string level, and DC power at the individual module. Each of these monitoring systems provides certain useful data for determining if the system is operating properly. However, these power monitoring systems are less useful for diagnosing issues when performance is inadequate.
Photovoltaic modules in the laboratory or manufacturing environment are often measured to provide a current-voltage curve (“IV curve”) that determines the module performance across the range of operating current and voltage points. The IV curve also varies with the amount of solar insulation and ambient temperature. IV curves provide a detailed insight to the internal performance of the photovoltaic module, which cannot be obtained easily once the system is installed in the field.
More recently, IV curve trace tools have been developed to enable photovoltaic maintenance personnel to diagnose issues in the field with installed photovoltaic systems. IV curve trace measurements can identify the cause of low performing modules such as soiling or shading, but they require highly-trained maintenance staff to use and interpret the measurements.
Published US application 2010/0071744 describes a Photovoltaic Installation with Automatic Disconnect Device. The DC disconnect device described therein uses a single DC disconnect with a control mechanism to disconnect in case of fire or other emergency. The single DC disconnect is located at the typical manual DC disconnect location between the string combiner and the converter. However, this system does not appear to offer any capability for string monitoring or diagnostics.